Contact lenses work by sitting atop the cornea and compensating for its flaws to achieve focus on the retina. Lasik permanently sculpts the cornea into the proper shape. "We use a machine to lift a thin membrane, or flap, which is a tenth-of-a-millimeter thick," Moadel explains. "We then just lift the flap and use the laser to reshape the surface underneath by a few thousandths of a millimeter. Then we simply put this flap back, moisten it, and it seals in place by itself, within a 12 to 24 hour period."
During office visits prior to the day of surgery, Moadel makes precise measurements of a patient's eyes, and feeds that information into a computer to determine how much corneal material to remove. "We actually measure patients two to three times for consistency," he says.
Once a flap in one eye has been peeled back, Moadel is ready to use the excimer laser, which destroys corneal material with ultraviolet light. "The laser is not burning, it's not heat," Moadel explains. "It's basically vaporizing. Every pulse of that laser removes a quarter-micron of cornea." In cases of myopia, microthin layers of cornea are eliminated to flatten its shape.
For hyperopia, a doughnut-shaped hole is made to create a more conical shape. On average, the laser procedure itself takes less than two minutes per eye. When it's done, patients spend a half-hour resting in a darkened lounge, then following one more examination, they're free to go home.
Know the Limits of LASIK
For most patients, LASIK is a vast improvement over previously available corneal surgery techniques in terms of pain, recovery time, and results. Overall, LASIK also has impressive rates of safety and effectiveness. In a 1999 study of LASIK performed on 1,013 eyes, 92 percent of patients gained 20/40 vision or better, and 47 percent were corrected to 20/20 or better. However, there are risks, limits to what Lasik can accomplish, and some important drawbacks: As with any invasive procedure, there is always a possibility of infection. According to the American Academy of Ophthalmology, complication rates vary from 0 to 5 percent in clinical studies, and 5 to 15 percent of patients return to their surgeon for enhancements to improve results.
- Short-term side effects following surgery can include pain, light sensitivity, and corneal swelling. In some patients these can last for several weeks. One of the most common complications of LASIK is wrinkling of the flap, causing distorted vision. It can usually be repositioned or treated with drugs, though in rare cases the flap may have to be re-cut.
- The majority of LASIK patients also report seeing glare or halos at night. This usually occurs in low light because the pupils widen beyond the area of the cornea corrected by the surgery. Most, though not all, find the problem subsides within six months, but the British Aviation Authority has discouraged pilots from undergoing LASIK for fear of permanently damaging their night vision. The U.S. military is still reviewing the long-term effects of Lasik.